Wheelchair base



FIG. 1 is a back perspective view.

FIG. 2 is a back view.

FIG. 3 is a front view.

FIG. 4 is a right side view.

FIG. 5 is a left side view.

FIG. 6 is a top view; and,

FIG. 7 is a bottom view.

The broken line showing of the tires and other frame elements is forillustrative purpose only and forms no part of the claimed design.

The ornamental design for wheelchair base, as shown and described. 